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Chapter 14.1 Notes
The Structure of the Atom
Lesson Objectives
 Define the atom.
 Explain how Democritus and John Dalton described atoms.
 Identify the instruments used to observe individual atoms
Vocabulary
 atom
Dalton’s atomic theory
proton
 nucleus
electron
atomic mass
 mass number
neutron
cathode ray
Atoms
Atoms are the smallest particles of an element that still have the chemical
properties of that element.
Scientists once believed atoms were the smallest particles of matter. With
the advancement of technology, it has become clear that atoms themselves
are made up of simpler (sub-atomic) particles.
Sub-atomic Particles
Atoms have positively charged protons and neutral neutrons inside a nucleus,
and negatively charged electrons outside the nucleus.
 Atoms of the same element have the same number of protons, which is
equal to an atom’s atomic number.
 Atomic number also describes the location of the element on the periodic
table. All the known elements are arranged on the periodic table based
on increasing atomic number.
 Because atoms are neutral, the atomic number equals the number of
electrons in the atom.
 Some atoms may have more electrons or fewer electrons than protons,
such atoms are called ions. Ions with more electrons are negatively
charged, while those with fewer electrons, positively charged.
Atoms of the same element may have different numbers of neutrons. Such
atoms are called isotopes. Isotopes of a given element have the same atomic
number, but different mass numbers.
Democritus and the Atom
The concept of the atom intrigued a number of scholars, both scientists and
philosophers. Although they could not observe individual atoms, they were still
able to propose ideas about the structure of the atom.
The Greek philosopher was among to suggest the existence of atoms. He
reasoned that atoms were both indivisible and indestructible.
Democritus however could not:
 Explain chemical behavior of elements.
 Did not have experimental support (not based on scientific method).
Dalton’s Atomic Theory
By using experimental methods, Dalton (1766-1844), an English chemist and
schoolteacher transformed Democritus ideas on atoms into a scientific theory.
Dalton studied the ratios in which elements combined in chemical reactions.
Based on the results, he formulated his now famous Dalton’s Atomic Theory.
Chemical reactions occur when atoms are separated from each other, join, or
re-arranged in a different combination. Atoms of one element can never be
changed into atoms of another element.
Sizing up the Atom
Atoms are very small.
 A pure copper coin / penny contains 2 x 10
22
atoms of copper.
 The world population is currently 7 x 10 9people
 There are 3 x 1012 (3 000 000 000 000) many atoms in the small coin
as there are people on the planet.
 10 000 000 (1x 107) copper atoms lined up side by side would only be 1
cm. long.
Individual atoms have been observed using scanning electron microscopes
(SEM)
 With the help of electron microscopes, individual atoms can be
manipulated to form new patterns.
 This new technology (nanotechnology) has great potential in medicine,
communication, energy and even space exploration.
Name____________________________________ Date_______
Ch. 14-1Lesson Check
1. How did Democritus characterize atoms? __________________
2. How did Dalton advance the atomic philosophy proposed by
Democritus__________________________________________
___________________________________________________
3. What instrument can be used to observe individual atoms?
___________________________________________________
4. Explain the main ideas of Dalton’s theory____________________
___________________________________________________
___________________________________________________
5. Why do the ideas on atoms proposed by Dalton are considered a
theory while those proposed by Democritus are not? ___________
___________________________________________________
6. According to Dalton’s theory, is it possible to convert atoms of one
element into atoms of another? Explain._____________________
___________________________________________________
7. A dozen of eggs have a mass of 635 g. Calculate the mass of a single
egg. (Show your work).
8. A sample of copper with a mass of 63.5 g contains 6.02 x 10 23
atoms. Calculate the mass of a single copper atom. (Show your work).
9. What are the three subatomic particles? What are the relative
charges and masses of each particle?
Particle
Symbol
Relative charge
Relative mass
10. Complete the table below
Name
Symbol
Atomic
Protons
Electrons Neutrons Mass
number
H
number
1
0
Sulfur
32
Ne
Sodium
10
11
12
Fe
Calcium
56
20